This invention generally relates to electric vehicles. More particularly, this invention relates to controlling a motor response in an electric vehicle based upon vehicle characteristics.
Conventional gasoline powered vehicles are designed to provide some consistency in motor response to manual manipulation of an accelerator pedal. The driver prefers to experience the same vehicle performance or motor response given the same pedal actuation. This is possible regardless of the level of fuel in the fuel tank or the temperature of the engine, provided that each is within an operable range.
More recently, electrically powered vehicles, or electric vehicles as they are commonly known, have been introduced. One drawback associated with electric vehicles is that the design does not automatically lend itself to providing a driver with a consistent motor response to a given accelerator actuation. For example, at initial start up, the electric motor temperature typically is lower than after the vehicle has been driven for some time. It is known that electric motors typically are unable to perform at the same level as the motor temperature increases. Motor performance typically is hindered by the motor""s ability to dissipate heat. Therefore, a driver typically experiences a more robust motor response to a given accelerator manipulation at vehicle start up compared to later after the vehicle has been driven for some time.
Another factor that hinders consistent motor response in an electric vehicle is the charge level in a fuel cell. Reduced charge levels can result in reduced motor performance even though there is enough power available to drive the vehicle.
There is a need for an improved control strategy to control the motor response in an electric vehicle so that power consumption is better managed and the driver experiences a more consistent motor response to a given actuation of the accelerator. This invention provides a system and method for controlling an electric vehicle motor response based upon vehicle characteristics such as motor temperature or fuel cell charge level.
In general terms, this invention is a system and method for controlling motor response in an electric vehicle that has a motor and a manually operable accelerator. The method of this invention includes several steps. First a vehicle characteristic, such as motor temperature, is monitored. The maximum power output available based upon the vehicle characteristic is determined. The motor response to a manipulation of the accelerator is adjusted based upon the determined maximum power. The adjustment to the motor response preferably is made to compensate for differences in motor performance as may be caused by the current state of the vehicle characteristic, such as motor temperature.